Part Sources

Metric Machine Screws for Atlas Locomotives

The four screws used to hold the Decoder Buddy onto the weights of Atlas locomotives are 1.6 mm x 4 mm metric machine screws.  They are fairly common and found on both Amazon and eBay.  These are the ones I purchased.


https://www.amazon.com/M1-6-1-6mm-0-35-Phillips-MonsterBolts/dp/B0789SYV49/ref=nav_ya_signin?keywords=1.6%2Bx%2B4%2Bmm%2Bmachine%2Bscrews&qid=1554891099&s=gateway&sr=8-7&th=1

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Thought about Digitrax and Scale trains installation by user

From a post by Dana L Dyer

What I did for the Milwaukee 156 Bicentennial; First, I waited a long time for ScaleTrains to make the model! I originally put a DH166MT on the Lok Sound/ScaleTrains board in the engine, but I wanted more. Hence the install of a SDHX186MT. You can load sound onto this decoder and have 8 light functions.
I started by removing the original board, and being careful to note which color wires were for what. The original board had good markings to help. Orange and Gray were for the motor, thicker red and black were from the track. The positive wire for all lights were thin red wires. Whites were for the headlights, yellows were for the number boards, black was for red class lights, blue was for white class lights, and green was for green class lights. The beacon had a red and black wire.
Once the main board was out, a put in a Buddy Board which is a board to take a 21 pin decoder and have breakout solder points for speakers, motor, and the 8 light outputs. Being my second one on a scale trains, I already knew I had to do some modifications. The board mount holes do not line up with the frames mounting holes, so I whittled away to enlarged the holes, being careful not to damage traces on the board. Note that the board has resistors on it already for LED lights. I’m going to ask about different resistors and mountings. I used delrin screws to hold the board to the frame. The ScaleTrains screws were too close to electrical contacts for my liking. (Not that I’ve ever had any problems with metal and electrical before!)
The frame itself is two pieces and comes apart easily. This will expose the area for speakers. I put a soundtrax 16x35mm speaker in that fits well. There was actually a plastic holder for two cube speakers, but I recently heard a ScaleTrains demo with the cubes...didn’t like it. There’s room in the wire channels to run speaker wires to the buddy board.
With the buddy board in and the track, speaker and motor wired, it was time for the first test. I found that the speaker wasn’t working. I found that the pins of the buddy fit loose into the decoder. I slightly bent a row of pins outward and this solved that problem. I taped the decoder down tight also. I loaded sound into the sound decoder and set the volumes I like.
Now to the lights; all of the wires were too short so I had to lengthen them. Also, since class lights and number wires come from each end, you really need to think about which one to connect first. The light board on the buddy would be a lot nicer if it was a little bigger so the solder pads weren’t so close together. When I tested, I found none of the rear lights worked. Further checking revealed a did a crap job on extending the common wire for the rear. I made a new extension and everything worked. Then I wired up the beacon, it’s original wires ran to a post mount which needed to be removed and then the wires extended.
Once the beacon tested good, I fully reassembled and then tested. Well, there was a problem. The engine ran in reverse while the front lights were on and vice versa. I went to change the direction CV, but realized a lot of other programming would have to be changed, so I decided to reverse the motor wires. When I got back to the motor wires, the correct color was already on the correct solder pad. I can only assume that the same happens to ScaleTrains as it did to LifeLike, that in the manufacturing process, sometimes wires get swapped. Once I switched the wires, it ran correctly.
Overall I am happy with this project. The engine runs smoothly with the digitrax decoders, all the lights work, and it’s another 3000HP of America ready to roll!


Note: We have  addressed a  lot of  Dana’s concerns.   This is my  reply.


Actually a lot of the things you mentioned have been addressed. I hope the hole issue works this time. We did move them out as far as we thought prudent. We did keep the traces away from the hole areas as far as was practical. I liked the Delrin screw idea and wondered if it was an M1.6 or M1.7 You can see the traces on either side of the board. There are no interior traces. That should leave some wiggle room for enlarging the holes. I wanted slots but the board manufacturer balked at the idea. We are changing over to a little taller 21-pin connector. The one we are using is NMRA spec but SoundTraxx and maybe Digitrax now may have a little thicker decoders os we are changing that. Don’t be afraid to squeeze the decoder home as well to get a good seat. Again my knowledge of Digitrax is limited but people had trouble with the SoundTraxx decoders until they seated them firmly. You’ll have to talk to the motor manufacturers for both of us! Why R wires colered??? Hmmmmm. Pad size on the small connector board will probably have to stay the same. What I’ve done to make them work for me is poke the wire through the hole solder it then cut the excess off. My LEDs come as prewired smd 0603s. The wire is at least 30 gauge and silicone so it doesn’t melt leaving me with good insulation.


And  now Dana’s  last  comment.


People, Nick from Nixtrains. See there are manufacturers that here what we say! There are a lot of possibilities for his Decoder Buddy boards and he is adapting them even more!

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Different resistances for LEDs, bulbs and lamps

Considering the Resistance - Options for Required Resistances On the Decoder Buddy

The original Decoder Buddy was designed for use with LEDs.  The LED current is set for about 6 ma,  Some applications require a different resistance on a particular or all the function outputs for a specific voltage and minimum current.  Lamps or bulbs are a good example.  Some lamps or bulbs require about 1.5 volts and a little more current than the LEDs.  Other lamps or bulbs can handle the full 12 volts to 14 volts provided by the decoder.  Still others may have resistors installed inline already and just need the 12 - 14 volts provided by the decoder.  I have heard of mixed applications of LEDs and bulbs as well!  Some decoders can also provide the different voltages requiring you to choose the appropriate decoder voltage or Decoder Buddy.


There are a couple of ways of dealing with these requirements on the decoder Buddy.  


I now offer a Decoder Buddy using 0 Ohm resistors that allow for the full 12 - 14 volt output of the decoder to the function outputs.*  Alternatively, for the 12 - 14 volt applications you can also remove the 2.2K resistors easily by placing a hot soldering iron next to the longitudinal axis, melt the solder and flick the resistor away.  This leaves two vacant solder pads.  You can solder a short piece of ca 24 gauge solid copper wire across the gap, the two pads that can be bridged with solder or you can solder a 0 ohm 0603 resistor onto the two vacant pads. 


I offer a Decoder Buddy using 750 Ohm resistors that are compatible with the 1.5 volt bulbs now also.*  Alternatively for the 1.5 volt applications you can remove the 2.2K resistors and replace them with 750 Ohm (or your particular resistance preference) 0603 smd resistors.  You can also add inline resistors and then use a 0 Ohm Decoder Buddy or execute the procedure above to eliminate the resistance from the Decoder Buddy. 


If you want to purchase the 0 ohm or the 750 ohm types, have a special need for resistance or for a particular configuration feel free to email your request or questions.   The price list and shipping costs are the same for the 0 ohm and the 750 ohm Decoder Buddys.  Other requests will be on a quotation basis.


The order form is not as versatile as I would like but it's money in our pockets....  Thanks for bearing with me.


* Due to the number and types of 21-pin decoders that are compatible with the Decoder Buddy and the current draw of different lamps and bulbs, I leave the determination of current loading of the decoder to you to calculate.  Do not exceed the current capacity of the discrete function output or the total output of the decoder.



The 2.2K resistors are labeled and in the same position on the original Decoder Buddys as shown.
The 2.2K resistors are labeled and in the same position on the original Decoder Buddys as shown.

tips and tricks

Reflow soldering for pads

Reflow soldering the motherboard and the wire leads is a good way to make a good solder joint.  I use a good quality solder and fine tipped soldering iron.  Heat the pad with the soldering iron and melt a small spot of solder on to the pad.  Tin the end of the wire with the solder.  Now you have a hand for the soldering iron and a hand to hold the wire.  Place the wire on the tinned pad and heat the solder until it melts.  Remove the soldering iron and allow the joint to cool.  If you don’t feel confident with this procedure find an old printed circuit board and practice removing components and solder wire to the newly vacated pads. 

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For the first time installation

Some further thoughts

There are pleanty of decoder installation videos on YouTube as well as magazine articles to give you ideas about ”how to .”  You might also find one that is specific to disassembly of your particular locomotive.  The only difference between Decoder Buddy and an 8 pad decoder is the size and the 21-pin Decoder fits into the 21 pin plug.


The large motherboard is one sided but to be conservative a piece of insulating (Kapton preferred) tape placed on the bottom of the Decoder Buddy before mounting if directly onto a metal surface is highly recommended.  When mounting with double sided foam tape the extra insulating tape is not required.  Electrical isolation of the electronics and the locom chassis is the goal.


I prefer to cut the connectors off any of the wires from the track, motor, speakers, lights or stay alive noting any polarities that are relevant.  I cut the wires close to the connextort to leave as much wire as I can for routing purposes.  Before I solder the wires onto the Decoder Buddy pads I cut them so that there is about ¼” extra.  An exception is the motor wire.  I prefer to leave it long and tuck it out of the way if possible.  The extra ¼” of wire keeps the installation neat and leaves a little play for contraction, routing or whoopses.  I also keep the leftover wire for later use.  It does come in handy!


Motor wires, motor wire colors and decoder boards have given me fits and wrong way starts more than once. Now I solder the track wires and speaker wires to the Decoder Buddy but only clamp the motor wires to the decoder buddy.  I test the direction on a program track to make sure the locomotive moves in the direction that I want it to.  If I need to change the direction of the motor I change the leads on the pads and then solder them onto the board.


There are three common ways to install the mother board.  If you are lucky you have tapped holes for screws.  The screws are most likely metric size (M3?).  Second, if you have a circuit board in place that has four tabs with soldering pads on both ends remove it.  If there is enough headroom (height) Scotch 2 sided foam tape works well To attach the Decoder Buddy.  The plastic clip should act as insulation if you want to use Kapton tape to secure the Decoder Buddy Directly to the plastic.  The third way would be a DC powered locomotive like an Athearn blue box or a Proto 1000 without a printed circuit board.  After you isolate the motor electricall you can place a piece of Kapton tape on the bottom of the Decoder Buddy for “isolation insurance” then use the Kapton tape to attach it to the motor.


Read articles, blogs and posts.  Model Railroad Hobbyist Magazine and https://model-railroad-hobbyist.com/recent-posts and it’s associated search box in the upper right hand corner have a wealth of information on upgrading locomotives.  You should find the price is right too!!!

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